A systematic approach to estimating the effectiveness of multi-scale IAQ strategies for reducing the risk of airborne infection of SARS-CoV-2

Abstract

The unprecedented coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has made more than 125 million people infected and more than 2.7 million people dead globally. Airborne transmission has been recognized as one of the major transmission routes for SARS-CoV-2. This paper presents a systematic approach for evaluating the effectiveness of multi-scale IAQ control strategies in mitigating the infection risk in different scenarios. The IAQ control strategies across multiple scales from a whole building to rooms, and to cubical and personal microenvironments and breathing zone, are introduced, including elevated outdoor airflow rates, high-efficiency filters, advanced air distribution strategies, standalone air cleaning technologies, personal ventilation and face masks. The effectiveness of these strategies for reducing the risk of COVID-19 infection are evaluated for specific indoor spaces, including long-term care facility, school and college, meat plant, retail stores, hospital, office, correctional facility, hotel, restaurant, casino and transportation spaces like airplane, cruise ship, subway, bus and taxi, where airborne transmission are more likely to occur due to high occupancy densities. The baseline cases of these spaces are established according to the existing standards, guidelines or practices. Several integrated mitigation strategies are recommended and classified based on their relative cost and effort of implementation for each indoor space. They can be applied to help meet the current challenge of ongoing COVID-19, and provide better preparation for other possible epidemics and pandemics of airborne infectious diseases in the future.

Respiratory infection risk-based ventilation design method

“…More meaningful approach to define an acceptable probability level for a specific room is to use an event reproduction number R as recommended in Refs. [ 3 , 30 ]. R is defined as number of new disease cases divided by number of infectors.…”

“…To keep the basic reproduction number R 0 < 1 of COVID-19 due to airborne transmission, indicating the disease spreading in population, R < R 0 because susceptible persons may be exposed to more than one event [ 30 ]. In the present analyses R = 0.5 was used.…”

“…Defining the acceptable infection risk level needs a specific effort because infection risk-based ventilation design has so far not been used in public indoor spaces. In principle, the risk assessment can be conducted in community, building, room, personal or even in the breathing zone level [ 30 ]. Very low risk levels may lead to solutions which are not feasible, as a building should be designed and operated according to its purpose and the activities conducted there.…”

A review of different ventilation modes on thermal comfort, air quality and virus spread control

“…Besides, the use of high efficiency particulate air (HEPA) filter in mixing ventilation systems was another important way to deal with the particles and viruses. It could achieve a maximum particle removal efficiency of 99.9%, which was comparable to the virus infection prevention and control ability of air conditioning systems with 100% fresh air [ 89 ]. However, its location should be set close to the personnel activity area to improve the collection efficiency, and the filter element should be replaced frequently within a permitted period [ 90 ].…”

“…To improve air quality and reduce the risk of infection, it was also important by combining various ventilation modes or physical measures. DV reduced the risk of infection by about 26%, while the integration of DV and zoning reduced the risk of infection by an average of 96% [ 89 ]. In addition, the combination of partial radiation systems with DV would help maintain indoor temperature gradients and reduce the risk of upper layer pollutants entering the respiratory zone [ 158 ].…”